1. Field of the Invention
The present invention relates to a backlight module control system, and more particularly, to a backlight module control system having a plurality of backlight sources.
2. Description of the Prior Art
Please refer to FIG. 1. FIG. 1 is a diagram illustrating a prior art backlight module control system 100. As shown in FIG. 1, the backlight module control system 100 includes an inverter 110 and a plurality of backlight sources 120_1-120_8, where the inverter 110 includes four output nodes and each output node is connected to two backlight sources. In the operation of the backlight module control system 100, in order to ensure a uniform luminance of a display panel, the luminance of each backlight source is required to be the same; that is, a current of each backlight source needs to be as similar as possible.
Because the conventional backlight source is a cold cathode fluorescent lamp (CCFL), and the CCFL has a negative resistance characteristic, when the current of the backlight source 120_1 increases, the temperature of the backlight source 120_1 also increases, and the resistance of the backlight source 120_1 decreases due to the increased temperature. Because the output voltages of the inverter 110 are constant, however, the current of the backlight source 120_1 continuously increases due to the decreased resistance. In addition, the backlight module control system 100 generally has a maximum output power limitation; that is, a limitation of the total currents of all the backlight sources. Therefore, if the current of the backlight source 120_1 continuously increases, the current of the backlight source 120_2 will decrease, further causing different luminance between each backlight source, causing the luminance-uniformity of the display panel to be degraded.
To solve the above-mentioned non-uniform luminance of the display panel, an external circuit is used to ensure that each backlight source has the same current. FIG. 2 is a diagram illustrating a backlight module control system 200 using transformers to balance the currents of the backlight sources. As shown in FIG. 2, the backlight module control system 200 includes a voltage source 202, a plurality of backlight sources 210 and a plurality of transformers 220. Primary sides of the transformers 220 are respectively connected to the backlight sources 210, and secondary sides of the transformers 220 are connected in series. Because the secondary sides of the transformers 220 are connected in series, the secondary side coils of the transformers 220 have the same current Is, further inducing the current Ip of the backlight sources 210 to be the same. In addition, a prior art backlight module control system 300 using capacitors to balance the current of the backlight source shown in FIG. 3 and a prior art backlight module control system 400 using inductors to balance the current of the backlight source shown in FIG. 4 can also be applied to solve the above-mentioned non-uniform luminance of the display panel issue. In addition, the backlight module control system 300 includes a driving circuit 302, a transformer 320, a plurality of backlight sources 310 and a plurality of capacitors C1-C8; and the backlight module control system 400 includes a driving circuit 402, a transformer 420, a plurality of backlight sources 410, a plurality of inductors L1-L4 and a plurality of capacitors C1-C4.
Because the above-mentioned backlight module control system 200, 300 and 400 need external circuits, the complexity of the inverter and the manufacturing cost are increased.